Re: How does \musicMap not return music?

[David Kastrup]

Simon Albrecht <address@hidden> writes:

> Hello,
>
> surely I overlooked something:
>
> I’m writing a function to truncate MMRs for rehearsal MIDI. This is
> the code so far:
>
> %%%%%%%%%%%%%
> \version "2.19.53"
>
> truncateRests =
> #(define-music-function (mus) (ly:music?)
>    (let ((trunc-rests (lambda (e) (if (music-is-of-type? e
> 'multi-measure-rest-event)
>                                      (ly:music-set-property! e
> 'duration (ly:make-duration -1))))))
>      (musicMap trunc-rests mus)))
>
> \truncateRests { \time 4/2 R\breve*10 }
> %%%%%%%%%%%%%%
>
> Now Lily complains on that, saying ‘document.ly:9:1: error: music
> function cannot return ##<unspecified>’. I’m puzzled – musicMap is
> itself a music function, so how could truncateRests not return music?

Because trunc-rests doesn't?

Its last expression should be e but instead is

(if ... (ly:music-set ...))

which evaluates to *undefined* .

-- 
David Kastrup